Comparison of Corneal Thickness by Dual Scheimpflug Analyzer and Ultrasound Pachymeter in Ectatic and Myopic Eyes
Purpose
To assess the agreement of central corneal thickness (CCT) measurements using dual scheimpflug analyzer (DSA) and ultrasound pachymeter (UP) in corneal ectasia and myopic eyes.
Methods
This study is a retrospective review of medical records and DSA scans. Forty-five eyes of 30 patients diagnosed with keratoconus (KCN) and 23 eyes of 23 patients with forme fruste keratoconus (FFKC) were compared with 96 eyes of 49 myopic patients evaluated for refractive surgery. The following parameters provided by the dual Scheimpflug system were used for analysis: central average pachymetry (0.0-4.0 mm), paracentral average pachymetry (4- 7 mm), peripheral average pachymetry (7-10 mm), thinnest pachymetry and its location. CCT was also measured by UP in all the 3 groups.
Results
DSA overestimated CCT in myopic (p<0.01), FFKC (p=0.04) and KCN (p=0.01) eyes compared to measurements obtained by UP but, with the application of correction factor (0.98) the mean CCT measured by UP and DSA were comparable. There was a significant linear correlation between UP and DSA in myopic (P<0.01), FFKC (P<0.01) and KCN (P<0.01) eyes. Bland–Altman plot found a strong agreement between the two instruments in all the 3 groups. The mean thinnest corneal pachymetry was significantly lower in KCN eyes compared to myopic eyes. There was significant de-centration of thinnest point in FFKC and KCN eyes.
Conclusion
Galilei measurements of CCT are well correlated with ultrasound pachymetry in myopic and ectatic eyes. After considering a correction factor equal to 0.98 for Galilei, its measurements are comparable to ultrasound pachmetry values.